Molecular flexibility of methylcelluloses of differing degree of substitution by combined sedimentation and viscosity analysis.

The flexibility/rigidity of methylcelluloses (MCs) plays an important part in their structure-function relationship and therefore on their commercial applications in the food and biomedical industries. In the present study, two MCs of low degree of substitution (DS) 1.09 and 1.32 and four of high DS (1.80, 1.86, 1.88 and 1.93) were characterised in distilled water in terms of intrinsic viscosity [h]; sedimentation coefficient (s020,w) and weight average molar mass (Mw). Solution conformation and flexibility were estimated qualitatively using conformation zoning and quantitatively (persistence length Lp) using the new combined global method. Sedimentation conformation zoning showed an extended coil (Type C) conformation and the global method applied to each MC sample yielded persistence lengths all within the range Lp(1/4)12-17 nm (for a fixed mass per unit length) with no evidence of any significant change in flexibility with DS.